1. Field of the Invention
This invention relates to a solid-state imaging device used in the field of imaging techniques and the field of measuring instruments and applied to, for example, an XY-address type MOS imaging element.
2. Description of the Related Art
In a solid-state imaging device for converting an image of an object to an electrical imaging signal, a dynamic range is increased in order to cope with various objects having a wide luminance distribution.
A device for increasing the dynamic range of the solid-state imaging device is disclosed in Published Unexamined Japanese Patent Application (PUJPA) No. 63-232591. In a method for increasing the dynamic range disclosed in the above application, a plurality of images each obtaining a different exposure period are non-destructively read out from non-destructive read-out imaging elements, and the plurality of images are added to each other on the outside of the imaging elements. Consequently, an image obtained from the plurality of images, has an increased dynamic range, and has wide luminance information from low luminance to high luminance.
In a conventional solid-state imaging device, a switching portion formed in a pixel is driven (turned on) to read a charge from the pixel as a signal and supply the signal to outside the solid-state imaging device. However, the conventional imaging device has a drawback in which thermal noise due to the on-resistance of the switching portion is mixed into the signal read out from the pixel to decrease the S/N ratio of the signal.
However, when the dynamic range is increased by the above method, a driving circuit for successively changing the exposure period and a circuit for summing a plurality of images are required; the structure of the device becomes complex and the size of the element is increased.